1. Field of the Invention
The present invention relates to a tuner integrated circuit and a television tuner using this integrated circuit.
2. Description of the Related Art
The circuit configuration and the relationship between the arrangement of terminals of a known tuner integrated circuit (hereinafter referred to as an “IC”) 30 and peripheral circuits are described below with reference to the schematic diagram of FIG. 3. As shown in FIG. 3, the IC 30 has sixteen terminals at each of the two opposing sides. Terminals No. 1 through No. 16 are provided for one side 30a, while terminals No. 17 through No. 32 are provided for the other side 30b. A plurality of peripheral circuits, such as a very high frequency (VHF) mixer circuit 31 and a ultrahigh frequency (UHF) mixer circuit 32, are disposed, as shown in FIG. 3, inside the IC 30. The balanced input terminals of the VHF mixer circuit 31 are connected to terminals No. 31 and No. 32, and the input terminal of the UHF mixer circuit 32 is connected to terminal No. 29. The balanced output terminals of the VHF mixer circuit 31 and the UHF mixer circuit 32 are connected to terminals No. 26 and No. 27.
Local oscillation signals are supplied from a VHF low-band oscillation circuit 33 and a VHF high-band oscillation circuit 34 to the VHF mixer circuit 31. The two resonance-circuit connecting terminals of the VHF low-band oscillation circuit 33 are connected to terminals No. 1 and No. 2, while the two resonance-circuit connecting terminals of the VHF high-band oscillation circuit 34 are connected to terminals No. 4 and No. 5. A local oscillation signal is supplied from a UHF oscillation circuit 35 to the UHF mixer circuit 32. The four resonance-circuit connecting terminals of the UHF oscillation circuit 35 are connected to terminals No. 6 through No. 9.
Channel-selection data is input into terminals No. 17 through No. 19 from a television receiver (not shown). This selection data is input into a phase-locked loop (PLL) circuit 37 and a band-switching-voltage generating circuit 38 via an interface 36. Local oscillation signals are input into the PLL circuit 37 from the oscillation circuits 33, 34, and 35, and also, the tuning voltage for controlling the oscillation frequencies is output to terminal No. 15. A reference signal is input into the PLL circuit 37 from a reference oscillation circuit 39. The oscillator connecting terminal of the reference oscillation circuit 39 is connected to terminal No. 16.
The band-switching-voltage generating circuit 38 generates a high/low-level switching voltage according to the input data. This switching voltage is used for switching the band and is output to terminals No. 23 through No. 25.
An intermediate frequency (IF) amplifier circuit 40 is a balanced type, and the two input terminals are connected to terminals No. 21 and No. 22, while the output terminals thereof are connected to terminals No. 11 and No. 12. Terminals No. 3, No. 10 and No. 28 are grounded, and a power supply voltage is applied to terminal No. 13 so as to be supplied to the individual circuits.
Peripheral circuits are also provided outside the IC 30. A VHF tuning circuit 41 is connected to terminals No. 31 and No. 32, and a UHF tuning circuit 42 is connected to terminal No. 29. The input terminals of an IF tuning circuit 43 are connected to terminals No. 26 and No. 27, while the output terminals thereof are connected to terminals No. 21 and No. 22.
A low-band resonance circuit 44 is connected to terminals No. 1 and No. 2, a high-band resonance circuit 45 is connected to terminals No. 4 and No. 5, and a UHF resonance circuit 46 is connected to terminals No. 6 through No. 9. An oscillation device 47, such as a crystal resonator, is connected to terminal No. 16.
With this configuration, the tuning voltage output from terminal No. 15 and the switching voltages output from terminals No. 23 through No. 25 are applied to the tuning circuits 41 and 42 and the resonance circuits 44, 45, and 46, and these elements are set to receive the channel designated by the input data. Then, a television signal of the selected band is input into the VHP mixer circuit 31 and the UHF mixer circuit 32 from the tuning circuits 41 and 42, and is converted into IF signal components. The IF signal components are output to terminals No. 11 and No. 12 via the IF tuning circuit 43 disposed outside the IC 30 and the IF amplifier circuit 40 disposed inside the IC 30.
According to the IC 30 configured as described above, when the reference oscillation circuit 39 oscillates, a reference oscillation signal appears at terminal No. 16. The reference oscillation signal has a frequency of about 4 MHz, and, in particular, the higher harmonics of this signal are transmitted to the other terminals located in close proximity with terminal No. 16, and superimpose on the signals and the voltages output from such terminals, thereby interfering with the normal reception. For example, the tuning voltage is output to terminal No. 15, which is located adjacent to terminal No. 16, and even a slight change in the tuning voltage disadvantageously modulates the oscillation frequencies of the oscillation circuits 33, 34, and 35.